1. Field of the Invention
The present invention relates to a developer regulating member that regulates a developer carried and conveyed by a developer carrier, and to a developing device, an electrophotographic image forming process cartridge, and an image forming apparatus including the developer regulating member.
2. Background of the Art
A developing device, in which a developer carried on a developer carrier is regulated by a developer regulating member and conveyed to a developing area where the developer carrier faces an image carrier, such as, a photoreceptor, has been widely used in an image forming apparatus, such as, a copying machine, a printer, a facsimile machine, or other similar image forming apparatuses. In the developing area, an electrostatic latent image formed on the image carrier is developed with a developer carried on the developer carrier. A developing device using a two-component developer containing toner and magnetic carrier includes a developing sleeve as a developer carrier. The developing sleeve includes a magnetic field generating member inside, carries a two-component developer thereon by a magnetic force generated by the magnetic field generating member, and conveys the developer to a developing area while rotating. An amount (i.e., a thickness) of the developer carried on the developing sleeve is regulated by a developer regulating member spaced apart from the surface of the developing sleeve while the developer passes through a gap formed between an edge of the developer regulating member and the surface of the developing sleeve. Such a developer regulating member is described, for example, in Japanese patent publication No. 6-064396.
At a developer regulating position, where a developer regulating member regulates a developer carried and conveyed by a developer carrier, heat is produced by the friction between the developer regulating member and the developer, the surface of the developer carrier and the developer, and between the developer particles. The rise in developer temperature typically decreases the developing ability of the developer and deteriorates the developer, resulting in a short useful lifetime of the developer. For example, when using a two-component developer including a toner and a magnetic carrier, the rise in developer temperature at the developer regulating position decreases the amount of toner charged, thereby deteriorating the developing ability of the developer. Further, external additives added to the developer typically become embedded in softened toner particles, thereby changing the shape of the magnetic carrier due to direct contact between magnetic carrier particles. As a result, the developer deteriorates.
Moreover, the rise in toner temperature in the developer may cause a so-called toner filming problem. Specifically, when the temperature of toner rises at the developer regulating position, the toner softens and fuses. In this condition, a film made of fused toner adheres to a surface of a developer carrier, thereby deteriorating the developing performance of the developer carrier. Therefore, it is desirable to provide a developer regulating member that efficiently prevents the rise in developer temperature caused by the heat produced at the developer regulating position, and to provide a developing device, an electrophotographic image forming process cartridge, and an image forming apparatus comprising such a developer regulating member.
Several techniques have been proposed to control the temperature rise of a developer at a developer regulating position. For example, published Japanese patent application No. 2001-235942 describes a developing device having a heat radiating surface in contact with the developer regulating member and a cooling device to cool the heat radiating surface. In this developing device, in order to make the temperature in the longitudinal direction of the developer regulating member uniform, a heat pipe is embedded in the heat radiating surface. Alternatively, a heat pipe can also be fixed to the developer regulating member.
Another example is the published Japanese patent application No. 2001-083799, which describes a developing device including a developer regulating member formed from a thin, sheet-shaped, hard plastic member such as, polyethylene terephthalate. The developer regulating member is deflected so as to bulge toward at least a developer carrier side. The bulge portion of the developer regulating member is deformed along the circumferential surface of the developer carrier. On the inner (rear) surface of the developer regulating member, a heat conduction layer made of a material having a higher heat conductivity than the plastic is formed. Alternatively, a plurality of protrusions made of a material having a higher heat conductivity than the plastic is formed on the inner surface of the developer regulating member.
An amount of developer having passed through a gap (hereinafter referred to as a “developer regulating gap”) between the developer regulating member and the developer carrier per unit area is referred to as an amount of developer to be scooped up. When the amount of the developer scooped up is large relative to a gap in a developing area where the developer carrier opposes the image carrier, developer particles are pressed against each other in the developing area. In this condition, frictional heat is produced due to shear stress, thereby fusing the developer and causing it to adhere to the surface of the developer carrier. When the amount of the developer scooped up is small, a sufficient amount of toner cannot be supplied to the image carrier, resulting in a decrease of image density. Therefore, to obtain a stable, high-quality image, an adequate amount of developer scooped up needs to be conveyed to the developing area.
The developer regulating member 110 illustrated in FIG. 1 has been widely used. The developer regulating member 110 is formed by bending a metal plate member along a bending line. A leading edge surface 111 of the developer regulating member 110 is provided opposite to a surface of a developing sleeve to regulate the amount of developer carried on the developing sleeve. Generally, the leading edge surface 111 is formed by a press cutting process, which causes the leading edge surface 111 to be uneven in its longitudinal direction. Thus, when using the leading edge surface 111 as a developer regulating part of the developer regulating member 110, the amount of developer scooped up tends to be uneven in the longitudinal direction of the developing sleeve. For this reason, the leading edge surface 111 is generally subjected to a secondary manufacturing process, such as, cutting and grinding, thus increasing the manufacturing cost of the developer regulating member.
FIG. 2 illustrates some developer in a space between the developer regulating member 110 and the developing sleeve 165. The leading edge surface 111 of the developer regulating member 110 is separated from the developing sleeve 165 by a developer regulating gap. As illustrated in FIG. 2, gap (a) between the leading edge surface 111 and the developing sleeve 165 at an inlet side is greater than gap (b) where the developer regulating member 110 is the closest to the developing sleeve 165. The gap between the developer regulating member 110 and the developing sleeve 165, from the location of gap (a) to that of gap (b), is in the shape of a wedge. When developer is conveyed into the wedge-shaped gap, developer particles are pressed against each other, thereby producing stress. This is known as a wedge effect, which generates a reaction force that is detrimental to the developer regulating member 110.
Generally, the developer regulating member 110 illustrated in FIG. 1 is fixed to a developing device at two end portions (right and left side end portions in FIG. 1) of a base part 112 such that the leading edge surface 111 opposes a developing sleeve. As illustrated in FIG. 1, the base part 112 includes an edge different from the edge including the leading edge surface 111. In this construction, the reaction force produced by the wedge effect is exerted on a center portion of the developer regulating member 110 rather than at both end portions (right and left side end portions in FIG. 1) and deforms a bent part around the center portion of the developer regulating member 110 in the developer conveying direction. When the leading edge surface 111 is displaced due to the deformation of the bent part around the center portion of the developer regulating member 110, the height of the developer regulating gap increases, thereby increasing the amount of the developer passing through the center portion of the developer regulating member 110 compared to that at both end portions. As a result, the amount of the developer delivered to the developing area where the developer carrier opposes an image carrier becomes uneven in the longitudinal direction of the developer carrier, thereby generating an uneven image density in the axial direction of the image carrier.
Thus, it is desirable to provide a developer regulating member that adequately and uniformly regulates the amount of developer carried on a longitudinal direction of the developer carrier and to provide a developing device, an electrophotographic image forming process cartridge, and an image forming apparatus such a developer regulating member.